Water begins flowing over Suicide Basin ice dam, NWS tells Juneau to finish flood prep

Water has started flowing over the top of the ice dam at Suicide Basin. The National Weather Service is telling residents along Mendenhall Lake and the Mendenhall River to finish their flood preparations now.

NWS Juneau issued the special weather statement at 8:35 a.m. Tuesday. The latest camera imagery and water level data from inside the basin showed a slight drop, a sign that water is spilling over the dam. "Now is the time to finalize your flood preparation for potential flooding impacts along the Mendenhall Lake and River," the statement said.

What happens next is not fixed. In the past, the weather service said, a release has taken up to six days to start after overtopping begins. The statement runs through 4:45 p.m. Tuesday, and the office said it will update it within eight hours.

The warning is not tied to a single storm. Suicide Basin, an ice-dammed basin alongside Mendenhall Glacier, fills with glacial meltwater and periodically releases it. That cycle of fill, overtopping, release and downstream flooding along the Mendenhall Lake and River corridor has prompted repeated preparedness efforts in Juneau.

The Mendenhall River is the downstream path for any release, and Juneau has spent the summer preparing for one. An earlier Alaska News article on the 2026 flood season noted that nearly 1,900 homes in the Mendenhall Valley sit inside the evacuation advisory area. Another reported that the U.S. Army Corps of Engineers finished the second phase of HESCO barrier work along the river in July. Officials have said monitoring and modeling improvements since 2023 should give the community more notice if the river rises to hazardous levels.

Juneau, in a newsroom statement describing the basin as full and overtopping, said residents near the river, "especially those to the west of Riverside Drive, are strongly encouraged to make an evacuation plan and prepare a go-bag in case of emergency."

The weather service is posting basin conditions and release updates at weather.gov/ajk/suicidebasin.